First extraction of the proton mass radius and scattering length |αρ0p|from ρ^(0) photoproduction  

作　　者：Xiao-Yun Wang Fancong Zeng Quanjin Wang Li Zhang 

机构地区：[1]Department of Physics,Lanzhou University of Technology,Lanzhou 730050,China [2]Lanzhou Center for Theoretical Physics,Key Laboratory of Theoretical Physics of Gansu Province,Lanzhou University,Lanzhou 730000,China [3]Institute of High Energy Physics,Chinese Academy of Sciences,Beijing 100049,China [4]University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Science China(Physics,Mechanics & Astronomy)》2023年第3期98-103,共6页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.12065014,and 12047501);the Natural Science Foundation of Gansu Province(Grant No.22JR5RA266);the West Light Foundation of Chinese Academy of Sciences(Grant No.21JR7RA201)。

摘　　要：As it involves the lightest physical states excited from the vacuum by the vector quark current,near-threshold ρ^(0)photoproduction is considered a possible way to research the proton radius and the absolute value of the scattering lengths of the ρ^(0)-proton interaction.In this study,under the assumption of a scalar form factor of dipole form,the value of the proton mass radius is calculated as(0.85±0.06) fm by fitting the differential cross section of the γp→ρ^(0)p reaction at near-threshold energy.For light vector meson photoproduction,because the exchange of a scalar quark-antiquark pair is not suppressed and should dominate the scalar gluon exchange,the radius we extract from ρ^(0)photoproduction is likely to represent the quark radius of the proton.This fact may explain why the value obtained in this study is very near the proton charge radius.Moreover,the absolute value of the ρ^(0)-proton scattering length |αρ^(0)p|=(0.31±0.06) fm is obtained for the first time within the vector meson dominance model.This result disobeys the rule that the absolute value of the vector meson and proton scattering length |αVp| increases with the meson’s mass,which can be attributed to treating the ρ^(0)meson as a point in the analysis.These results provide useful theoretical information for an in-depth understanding of proton structure and the proton-vector meson interaction.

关 键 词：nucleon radius scattering length gravitational form factor meson photoproduction 

分 类 号：O572[理学—粒子物理与原子核物理]